It has heretofore been common to electrically stimulate nerves for various therapeutic purposes, and medical practitioners have heretofore used electrical stimulation for stimulating muscle activity, relieving pain, and producing sensation, among other therapeutic purposes.
The sequence of effects produced by electrical stimulation, as its intensity is increased, is known to generally follow a pattern of a perception of an electrical sensation (usually tingling), an increase in sensation, fasciculation muscle contraction, pain, and then injury in the form of electrical burns or cardiac arrhythmias.
While therapeutic effects often occur while stimulation is applied with a continuous intensity below that necessary to produce muscle contraction it should be remembered that exceptions do occur to the general effect pattern such as, for example, when a DC current is applied and slowly increased in intensity, muscle contraction cannot be obtained, though the other effects occur in the same order.
Electrical stimulation has been attempted and/or realized through use of a wide variety of electrical waveforms and these waveforms have ranged from a purely DC (galvanic) current or voltage to many different combinations of electrical pulses of various shapes and durations. While at least some such waveforms have provided some degree of desirable effect, the results achieved have been random with no clear understanding of how optimization might, or could, be achieved.
As brought out hereinabove, stimulation has also been made to occur with many different types of pulses, and pulse pairs that include both positive and negative pulses have heretofore been suggested (see, for example, U.S. Pat. Nos. 2,375,575, 3,946,745, 4,237,899, and 4,256,116). While these patents suggest that bi-phased pulse pairs can be utilized for therapeutic purposes, there is no teaching in these patents of devices or methods that are shown to optimize stimulation. Such optimization is important, however, to achieve results with minimum power and maximum effect on functions of the body controlled by the fibers specifically stimulated.